Added a Glossary entry (with diagrams) explaining the difference in accuracy...

Added a Glossary entry (with diagrams) explaining the difference in accuracy between the new formula for calculating the Camera detector resolution compared to the old way.  References #476.

git-svn-id: http://subversion.wr.usgs.gov/repos/prog/isis3/trunk@7016 41f8697f-d340-4b68-9986-7bafba869bb8